The present invention relates to rotation sensors, such as gyroscopes, and particularly to a fiber optic rotation sensor which has an extended dynamic range.
Fiber optic rotation sensors typically comprise a loop of fiber optic material to which light waves are coupled for propagation around the loop in opposite directions. Rotation of the loop creates a relative phase difference between counter-propagating waves, in accordance with the well known "Sagnac effect", with the amount of phase difference corresponding to the velocity of rotation. The counter-propagating waves, when recombined, interfere constructively or destructively to produce an optical output signal which varies in intensity in accordance with the rotation rate of the loop. Rotation sensing is commonly accomplished by detection of this optical output signal.
Various techniques have been devised to increase the sensitivity of fiber optic rotation sensors to small rotation velocities. However, most of these techniques have not been useable for detecting very large rotation velocities because the output functions tend to repeat themselves at various velocities of rotation. As a result, the output signal cannot be utilized to determine which of those possible rotation velocities having the same output signal waveform is responsible for the particular output signal waveform observed.
Thus, it would be a great improvement in the art to provide a phase modulation technique wherein rotation could be accurately and reliably sensed over a very broad range of rotation velocities. Such a technique, and means for its accomplishment are described herein.